Satellite radio navigation makes it possible to obtain the position of a receiver by a resolution similar to triangulation, by using the pseudo-distances measured from signals sent by satellites.
To receive signals originating from the satellites, it is possible to use, for example, a receiver provided with an antenna of CRPA (Controlled Radiation Pattern Antenna) type.
FIG. 1 represents the input stage of a receiver of satellite signals 100 according to the prior art. Conventionally, a receiver 100 provided with a CRPA antenna 101 comprises:                an antenna 101 comprising a plurality of sensors 102,        for each sensor 102, an analogue channel for filtering, amplifying, converting to intermediate frequency and digitizing the signals originating from the sensor (RF—radio frequency—and ADC—analogue-digital converter—block supplying a digitized signal Ssensor, M representing the number of sensors of the antenna),        a digital antenna processing common to all the sensors (not represented in FIG. 1), which filters and combines the digitized sensor signals, which may be specific to each satellite direction,        for each satellite signal, a digital signal processing (not represented in FIG. 1) which performs the demodulation (demodulation of the carrier and of the Doppler and unspreading by correlation with a local code) of the signal resulting from the digital antenna processing.        
To enhance the performance of a CRPA antenna, it is known to implement different antenna processing methods. Some of these methods need the following data:
(i) the direction of the satellites in the antenna coordinate system (or sensor coordinate system), and
(ii) phase shift biases βsensor induced by the analogue channels between the phase centre of each sensor and the analogue-digital converters.
The direction of the satellites is perfectly known in the TGL (local geographic trihedron, north, east, vertical coordinate system centred on the position of the receiver) coordinate system from ephemerides or almanacs. To deduce therefrom the direction in the sensor coordinate system, it is essential to know the attitude of the antenna relative to the TGL. The attitude is the orientation of the antenna relative to the three axes of a reference coordinate system, in this case the TGL coordinate system.
The attitude of the antenna is conventionally given by an attitude and heading inertial reference (AHRS—Attitude and Heading Reference System) hybridized with other sensors (anemometry, GPS, Doppler radar, etc.) or by a stand-alone inertial reference (IRS—Inertial Reference System).
It is also possible to determine the attitude of the antenna from the satellite signals themselves, which arrive with different phase shifts on the sensors, according to the incident direction.
In all cases, the attitude of the antenna, supplied by an inertial reference or identified from the satellite signals, makes it possible to determine the direction of the satellites in the antenna coordinate system.
As indicated above, some signal processing methods also require the knowledge of the biases of the sensors βsensor.
Methods are known for identifying the biases of the sensors in the factory. However, this increases the cost of production of the equipment (calibration means and time spent) and do not make it possible to compensate for the ageing of the sensors which induces a variability of the bias.
It is also possible to provide the antenna electronics with an in-flight self-calibration device with its own calibration signal, but this does not make it possible to include the bias due to the sensor alone (the calibration signal being introduced between the antenna and the analogue reception subsystems, the calibration cannot therefore determine the defects in the sensors of the antenna) and increases the costs of the equipment because of the additional hardware.
Systems are known like those presented in the U.S. Pat. No. 5,446,465, which use double differences of the phase measurements which make it possible to completely eliminate the biases of the antenna sensors, in particular the (predominant) portion that is independent of the satellite directions (therefore common to all the satellite measurements). Thus, in this case, the search for the minimum of the minimization criterion for the root mean square value applied to the deviations between the measured double differences and the theoretical double differences must lead to zero for the correct attitude hypothesis. In these systems, the biases are processed as stray effects, which are tried to be disregarded.